Spiral-four quad structure

ABSTRACT

This application discloses a spiral-four quad conductor structure in which a desired square geometry is maintained by a thermoplastic filler. Four conductors are drawn through a filler bath and thereafter, through a circular die. Cooling of the filler assures maintenance of the quad into its desired geometry, as well as providing waterproofing for the quad.

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OTHER REFERENCES Biskeborn et al. Jelly Blend Waterproof Cable in BellLab. Records, March 1969, pp. 71- 75 Primary Examiner-E. A. Goldberg[54] SPIRAL-FOUR QUAD STRUCTURE 6 Claims, 8 Drawing Figs.

Attorneys-R. J. Guenther and Edwin B. Cave ABSTRACT: This applicationdiscloses a spiral-four quad conductor structure in which a desiredsquare geometry is maintained by a thermoplastic filler. Four conductorsare EMM M P/Z 3 7 0 0 4i lib- /.ll.l 4/0 3 74" In m3 m "2 n a m u u u S.1 o M mm al Q U h 1 ll. 2 0 5 55 .l. [l

[56] References Cited UNITED STATES PATENTS 1/1968 327,459 9/1885Spalding.......................

drawn through a filler bath and thereafter, through a circular die.Cooling of the tiller assures maintenance of the quad into l74/l l3 Xits desired geometry, as well as providing waterproofing for 174/113 Xthe quad.

PATENTED nm 5 IBYI SHEET 1 BF 2 /Nl ENTO/? By J M. PEACOCK A @M. 8. 1M

ATTORNEK SPIRAL-FOUR QUAD STRUCTURE FIELD OF THE INVENTION Thisinvention relates to multiconductor telephone cable and morespecifically to a spiral-four quad structure and its relatedmanufacturing methodology.

BACKGROUND OF THE INVENTION As an alternative to the widely used twistedpair in multipair telephone cable, the so-called spiral-four quad has intheory many advantages. It is, for example, much less susceptible totwist length distortion since the four wires are nested in a squaregeometry rather than lying flat as do pairs. Also, crosstalk-causingelectric fields have less influence on a quad than on a twisted pair.The quad additionally provides a significant space saving per circuit ascompared to twisted pairs. Even beyond this, it is possible by the useof the phantom circuit to provide still further increase in circuitcapacity.

The widespread use of spiral-four quads in the United States has,however, been impeded by the extreme difficulty in achieving the desiredlow side-to-side capacitance unbalance within the quad. This problemtraces to the tendency of quads with handling or usage to assumegeometries other than the required square configuration. The typicalsolution heretofore has been to incorporate a properly sized filer suchas a string in the center of quad structure or, as disclosed in US. Pat.No. 3,364,305, incorporate a webbing between opposite conductors in thestructure.

The present invention addresses the problem of providing a highly stablesquare configuration in a spiral-four quad while reserving full freedomto apply shielding. Additionally the invention involves concurrentlysupplying the basic building block for a cable which is waterproof.

The principal inventive objects are:

to enhance the long-term geometric stability and hence the transmissionperformance of the spiral-four quad conductor;

to accomplish the above objects without sacrifice of useful shieldingconfigurations; and

at the same time, to utilize the stabilizing medium as the vehicle forcable waterproofing.

SUMMARY OF THE INVENTION The desired square geometry of a spiral-fourquad is maintained, pursuant to the broad inventive teaching, by thepresence of a tacky, thermoplastic material completely filling theinterstitial space between four polyethylene insulated conductorsarranged in square configuration, and the presence of sufiicientinwardly directed binding forces on the conductors to prevent theirspreading outwardly in later use and handling.

Any departure from the square configuration requires either a reductionin the interstitial cross section area or a spreading outwardly of atleast one of the conductors. Preventing the latter substantiallyprevents the former in the instant invention since the area reductioncannot occur without expulsion of the filler material therefrom. Theinterstitial material is, however, too tacky at normal operatingtemperatures to flow. The area accordingly does not contract, and theinsulated conductors therefore retain their original square geometry.

Numerous expedients, singly or in suitable combinations, can provide therequisite inwardly directed forces on the insulated conductors of eachspiral-four quad. The same thermoplastic material, for example, is inone embodiment applied to surround the exterior of the quad in acircular geometry. For further example, a shielding tape or binderapplied around the quad supplies the retaining force. Further still,numerous such quads can be assembled in a unit, the interstices of whichin turn are similarly filled, with the entire unit then jacketed.

An example of suitable filler material is a 3:1 by weight mixture ofpetroleum jelly and a thermoplastic polymer of high average molecularweight. Numerous examples of such material are disclosed in thecopending application of M. C. Biskeborn et al. Ser. No. 780,314 filedDec. 2, 1968 and assigned to applicant's assignee; and this disclosureto the extent pertinent is hereby incorporated by reference into theinstant specification. These materials when used pursuant to the presentteachings supply the added advantage of waterproofing to the end ofstabilizing the quads transmission performance.

In a particular inventive embodiment embracing methodology, fourpolyethylene-insulated conductors are drawn through a bath ofthermoplastic filler and, thereafter, through a properly sized circularpolishing die whose diameter is chosen to just pass the four conductors.The conductors thus are forced into a symmetrical square geometry, withthe filler flooded into the configurations interior as well as in theexterior interstices. On emerging from the polishing die, the fillersolidifies, freezing the quad into its desired geometry.

Shielding in the form, for example, of a longitudinally applied metallictape advantageously is formed over the quad, for example aftertheabove-mentioned cooling stage. Thereafter, a suitable number of suchquads are combined as piece parts to form a multipair-communicationscable.

The filler used in constructing the spiral-four quad is characterized,pursuant to the invention, by a low dielectric constant, low moisturepermeability, adequate body and tack at the range of temperatures to beencountered in service so as to hold the quad in position andflexibility at reduced tempera tures.

The invention and its further objects, features, and advantages will bemore fully apprehended from a reading of the following detaileddescriptions embracing illustrative embodiments.

THE DRAWING FIGS. 5A, 5B, and 5C depict sectional views through the bathat three points.

lLLUSTRATIVE EMBODIMENT FIG. 1A shows in broad schematic form theessential elements for the manufacture of a spiral-four quad pursuanttothe present invention. For illustration's sake, the making of but asingle quad is described, it being understood that manufacture ofnumerous such quads concurrently is both feasible and desirable.

As shown in FIGS. 1A and 1B, polyethylene-insulated conductors 2, 4, 5,6 are supplied from sources such as reel 1 to a filler bath 3. Allconductor sources are similar to reel 1. Advantageously, each is rotatedin the direction of arrow 7 while paying out their conductor. The amountof rotation can, for example, be one turn for each 15 diameters ofadvance. In this fashion, possible eccentricities of the insulation ofeach of the conductors 2, 4, 5, and 6 with respect to the center wireare averaged out and thus compensated for, to avoid capacitanceunbalances that might otherwise result. Another way of avoiding diameterdifferences and eccentricities is to use on all reels insulatedconductor from contiguous section of the output of a given extruder.This is generally termed matched-insulated conductor. Preferably also,the wire from which the conductors are made is matched in the samesense. I

The bath 3 consists of an end plate 8, internal guide rings such as 9,and 10, and a circular die 11, which, for example, can be a properlysized orifice in the end 12 of bath 3. Heatedtherrnoplastic filler isintroduced into the interior of bath 3 through pipes 13a, 13b, 13c, 13d,13e, 13], 133 from suitable sources 40, 41. The filler when used withpolyethylene-insulated wire should have a dielectric constant in therange of 2.2 to 2.4. It should be readily flowable at temperatures of,say. C. to facilitate its application to and around the conductors inbath 3 while they are moving at a rate of about a foot per second. Theadherence to the insulation must be firm at all temperatures below 120C. particularly those in the usual operation range from 50 C. to C. orless. Material rigidity and techniques in this range must be sufficientto prevent oozing or flowing of the material from between thecontacting-insulated conductors once they are held in a square geometry.At low temperatures, the material must remain flexible.

The end plate 8 in bath 3 receives the conductors 2, 4, 5, and 6 throughports 14, l5, l6, and 17 respectively. The orifices are of a diameter topass the conductors without allowing filler inside to escape. Entranceports 14-17 are separated sufficiently to space the conductors 2, 4, 5,6 as they enter the bath 3. In FIG. 1B, because of the perspective, onlyorifices I5, 17 and insulated conductors 4, 6 are shown.

The filler is, for example, a blend of 80 to 89 percent petroleum jellyand 1 l to 20 percent of crystalline-olefin polymer having an averagemolecular weight greater than 20,000 and a dielectric constant of from2.2 to 2.4 at room temperature. The olefin polymer is one of a groupconsisting of ethylene and a-olefins, for example, polyethylene,polybutene, or polypropylene. The filler temperature in the bath isabout 120 C., but on exiting is rapidly cooled.

The guides 9, within bath 3 are, for example, circular rings mounted onlegs such as 18. The guide diameters are chosen to coerce the conductors2, 4, 5, 6 in stages toward each other as they are drawn through theviscous filler, so that ultimately at forming die 1 1 the conductorswill have assumed a symmetrical square configuration. Typical of thestages through which the conductors 2, 4, 5, 6 pass are theconfigurations of FIGS. 5A, 5B, and 5C. In FIG. 5C, it is seen that theconductors, by virtue of their closely controlled insulationouterdiameter interacting with the appropriately sized form ing die 11, arenecessarily forced into the desired square contacting geometry, in whichthe conductor centers from the comers of a square and the insulationsurfaces are in contact.

On exiting from bath 3, the now-formed quad, designated 20, is envelopedinternally and externally in the filler compound and has a circularcross section. Now, the requisite spiral in either direction such asdenoted by the arrow 21 in FIG. 2 is applied to the quad. This isachieved through a conventional expedient such as rotating the takeupreel 22 in the direction of arrow 23 in FIG. 1A. The reel 22 itself isdriven in the direction of arrow 24 for takeup purposes by a suitablemotor, not shown. Reel 22 is mounted in the reel fork assembly 25 thatin turn is fastened to shaft 26, the latter being rotated to produce thedesired quad twist.

In the instant embodiment, longitudinal shielding tape 29 is applied toquad after the filler is applied and while the quad is being twisted andtaken up. The tape apparatus as shown FIG. 1 consists of a shieldingtape supply reel 27 suitably mounted in rigid fashion by arms 28 uponfork 25. The tape 29 and quad 20 pass in unison through a conventionalshoehom forming die 30 which is also rigidly supported from fork by armsa.

It can be advantageous to supply filler into bath 3 from an additionalentrance port 13g located in the region of end plate 8 between theentering conductors 2, 4, 5, 6. This location supplied filler tofacilitate complete filling of the interstitial region between theconductors. Entrance port 13g can also be used to supply a differentfiller material from that destined for the quad s outer surface. Forexample, a less viscous or harder filler in the interstitial regionbetween conductors may be desired to provide added rigidity and securityto the square geometry.

Filling is further enhanced by coercing the wires together in stagesthrough guides 9 and 10. In this way, as the conductors draw together,the filler in the interstitial region is compacted and forced outwardlyinto the main body of filer in the bath. Then, as the quad passesthrough the polishing die 11, the filler in the inner region undergoes aslight amount of final compacting. The filler remaining in theinterstitial region is the maximum amount compactible into that region.

Shleldmg tape incorporated into the process may be as exemplified inFIG. 18. There, the tape results in a quad having the configurationillustrated in FIG. 2. FIGS. 3 and 4 illustrate two further possibleshielded structures. In FIG. 3 a shielding tape 29a has been applied asa loop around the diametrically opposite conductors 14, 17. In FIG. 4 ashielding tape 29b has been applied in figure-eight fashion aroundopposed conductors l4, 17. In each case, the tapes 29a and 29b areapplied by machinery advantageously located (but now shown) within thebath 3. In this fashion, the interstitial area between the conductorscontinues to be occupied by the filler, with both the shielding tapes29a or 29b and the conductors surrounded with the filler.

The shielding tape 29 of FIG. 3 also supplies inwardly directed forceupon the conductors 2, 4, 5, 6. Other tapes, such as plastic ribbonbinders, are also capable of providing this force. The binding forcemust be sufiicient in all cases to prevent separation of the insulatedconductors 2, 4, 5, 6that is, to prevent any two which are in contactwith each other from losing that contact.

The second important aspect of the thermoplastic filler, as taughtgenerally in the aforementioned Biskeborn at al. application, is as awaterproofing agent for each of the quads 20. Reference to thestructures of FIGS. 3 and 4 reveals that the filler 32 sufficientlyenvelops the conductors to render impossible the intrusion of any waterwithin the structure. This then assures the stable performance of thequad in its application as a transmission line. Additionally, by afurther filler flooding operation during a subsequent step (not shown)of assembling a multiquad cable from numerous such quads, thewaterproofing of the cable itself is assured. This is of advantage toenhance the long-term maintainability of the cable, particularly whenburied in the ground, or in an underground conduit.

The spirit of the invention is embraced in the scope of the claims tofollow.

What is claimed is:

l. A spiral-four quad comprising:

four matched insulated conductors arrayed in square, contactingconfiguration;

a thermoplastic, waterproof, tacky material completely filling the spacebetween said conductors; and

means binding said insulated conductors together with a force sufficientto prevent their separating outwardly.

2. A spiral-four quad comprising:

four matched, insulated conductors arrayed in square, contactingconfiguration;

a thermoplastic, waterproof, tacky material filling the space betweensaid conductors, said material also completely covering the exteriorsurfaces and completely filling the exterior interstices of said fourconductors; and

means binding said insulated conductors together with a force sufficientto prevent their separating outwardly.

3. A spiral-four quad pursuant to claim 2 wherein the outer surface ofsaid material covering said exterior interstices is circular in crosssection.

4. A spiral-four quad in accordance with claim 3, further comprising atape binder applied directly over said outer surface.

5. A quad in accordance with claim 2 in which said insulation ispolyethylene and said material is further characterized by a dielectricconstant of from 2.2 to 2.4 low viscosity at temperatures of about 120C., tackiness at temperatures below about 50 C. and flexibility attemperatures below freezing.

6. A quad in accordance with claim 2 in which said material comprises ablend of to 89 percent petroleum jelly and I l to 20 percent ofcrystalline olefin polymer having a weight average molecular weightgreater than 20,000 and a dielectric constant .less than 2.4 at roomtemperature, wherein said polymer is one of a group consisting ofethylene and a-olefins.

1. A spiral-four quad comprising: four matched insulated conductorsarrayed in square, contacting configuration; a thermoplastic,waterproof, tacky material completely filling the space between saidconductors; and means binding said insulated conductors together with aforce sufficient to prevent their separating outwardly.
 2. A spiral-fourquad comprising: four matched, insulated conductors arrayed in square,contacting configuratiOn; a thermoplastic, waterproof, tacky materialfilling the space between said conductors, said material also completelycovering the exterior surfaces and completely filling the exteriorinterstices of said four conductors; and means binding said insulatedconductors together with a force sufficient to prevent their separatingoutwardly.
 3. A spiral-four quad pursuant to claim 2 wherein the outersurface of said material covering said exterior interstices is circularin cross section.
 4. A spiral-four quad in accordance with claim 3,further comprising a tape binder applied directly over said outersurface.
 5. A quad in accordance with claim 2 in which said insulationis polyethylene and said material is further characterized by adielectric constant of from 2.2 to 2.4 low viscosity at temperatures ofabout 120* C., tackiness at temperatures below about 50* C. andflexibility at temperatures below freezing.
 6. A quad in accordance withclaim 2 in which said material comprises a blend of 80 to 89 percentpetroleum jelly and 11 to 20 percent of crystalline olefin polymerhaving a weight average molecular weight greater than 20,000 and adielectric constant less than 2.4 at room temperature, wherein saidpolymer is one of a group consisting of ethylene and Alpha -olefins.